1. Field of the Invention
The present invention relates to a reciprocating compressor having double headed pistons with a plurality of pairs of cylinder bores formed to accept the heads of the pistons to compress a coolant gas.
2. Description of the Related Art
This type of compressor is disclosed, for example, in Japanese Unexamined Patent Publication (Kokai) No. 6-101638. In this type of compressor, as shown in FIG. 8 of the attached drawings, a drive shaft 101 is rotatably supported by a cylinder block 112, and the cylinder block 112 has a plurality of pairs of cylinder bores 102 arranged around the axis of the drive shaft 101 with each pair including coaxially extending front and rear cylinder bores 102. Double headed pistons 103 are arranged in the respective pairs of cylinder bores 102 to form compression chambers 106 with both ends of the pistons 103. The pistons 103 are reciprocatingly moved by a swash plate 104 attached to the drive shaft 101 to compress a coolant gas.
In the compressor of FIG. 8, the cylinder block 112 has valve chambers 108 arranged in the corresponding front cylinder bores 102 and rear cylinder bores 102, and rotary valves 105 are arranged in the valve chambers 108, the rotary valves 105 being supported by the drive shaft 101. Suction passages 107 are arranged in the rotary valves 105, and suction ports 111 are arranged in the cylinder block 112 adjacent to the cylinder bores 102, for introducing a coolant gas from the suction chamber (crank chamber) into the compression chambers 106 during suction strokes.
In this compressor, it is not necessary to arrange suction valves for every compression chamber 106, and the structure of the compressor can be simplified. However, in this compressor, wear may occur in the sliding inner and outer surfaces of the valve chambers 108 and the rotary valves 105, so that the sealing function declines.
Such a sealing problem may be solved by a compressor disclosed, for example, in Japanese Unexamined Patent Publication (Kokai) No. 6-58252. In this type of compressor, as shown in FIG. 9 of the attached drawings, rotary valves 105 and valve chambers 108 are formed in a tapered shape, and springs 109 are provided for urging the rotary valves 105 into contact with the valve chambers 108. When wear occurs on the sliding inner and outer surfaces of the valve chambers 108 and the rotary valves 105, the rotary valves 105 advance further into the valve chambers 108 to absorb the wear, and the sealing function is maintained.
In addition, the outer surfaces of the rotary valves 105 in the compressor of FIG. 9 are tapered, and a higher pressure acts obliquely on the outer surfaces of the rotary valves 105 via the suction ports 111 if the pressure in the compression chambers 108 rises abnormally due to a liquid compression, for example. The high pressure acting on the rotary valves 105 includes a component of a force in the axial direction of the rotary valves 105. Therefore, the rotary valves 105 are moved in the direction of the arrow against the springs 109 to produce a clearance between the rotary valves 105 and the valve chambers 108, with the result that the pressure in the compression chambers 108 is released via the suction ports 111 into the compression chambers 108. On the other hand, the pistons 103 are subjected to a compression reaction force by the pressure in the compression chambers 108, and the drive shaft 101 also receives the compression reaction force via the pistons 103 and the swash plate 104. However, since the higher pressure is released, an excessive compression reaction force acting on the drive shaft 101 is mitigated.
In addition, a prestressed spring (not shown) is provided in the compressor for urging the drive shaft 101 in an axially predetermined direction to prevent the drive shaft 101 from undesirably oscillating. However, the degree and the timing of the released pressure from the front compression chambers 108 may be different from those from the rear compression chambers 108 because it is not usual that an amount of liquid coolant remaining in the front compression chambers (causing a liquid compression) is identical to an amount of liquid coolant remaining in the rear compression chambers. Therefore, there is a possibility that the compression reaction force acts on the drive shaft 101 in the direction in reverse to the direction of the urging force by the spring. The drive shaft may thus undesirably oscillate, so noise in the compressor may increase.